LLNL-PRES-680527This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC

High-magnetic field suppression of antiferromagnetism in USb2

Ryan L. StillwellLawrence Livermore National Laboratory

Physical Phenomena at High Magnetic Fields VIIITallahassee, FL January 7, 2016

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Collaborators

Jason Jeffries

Lawrence Livermore National Laboratory

NIST Center for Neutron Research and U. MarylandNicholas Butch

I-Lin Liu

Marcelo Jaime

Neil Harrison

NHMFL-Pulsed Field Facility Los Alamos National Laboratory

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Outline

Why USb2?

Part One: Magnetostriction—AFM suppression seen via fiber Bragg

dilatometer

Part Two: Magnetization—AFM suppression confirmed via extraction

coil magnetometer

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Antiferromagnet below TN=202K— High energy scales involved

Highly anisotropic, quasi-two dimensional structure

U 5f-electrons are hybridized

Fermi surface reconstruction going from paramagnetic to antiferromagnetic phase

Introduction to USb2

D. Aoki et al., Phil. Mag. B, 80, 1517 (2000)

Paramagnetic

Antiferromagnetic

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D. Aoki et al., Phil. Mag. B, 80, 1517 (2000)

USb2 AFM unit cell is 2x the chemical unit cell

AFM unit cell

chemical unit cell

Paramagnetic

Antiferromagnetic

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Part One

Magnetostriction

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Fiber Bragg dilatometer avoids eddy current heating and enables measurements in pulsed fields

c-axis//H1 mm a-b plane//H

Had to stack 6 crystals

a) b) c)

d)

R. Daou et al., RSI, 81, 033909 (2010)M. Jaime et al., PNAS, 31, 12404 (2012)

A. Grockowiak, in preparation

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Thermal contraction along a-b plane confirms AFM transition at TN= 202K

TN

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USb2 does not show AFM transition in magnetostriction along the a-b plane

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vertical offset for clarity

USb2 shows AFM transition in magnetostriction along the c axis

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H-T phase diagram of AFM-PM transition observed via magnetostriction along the c axis

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What is the high-field magnetic structure?Is there a change from 2nd to 1st order at lower T?

vertical offset for clarity

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Part Two

Magnetization

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USb2 sample loading for extraction coil magnetometry

Sample with c-axis coming out of the picture

Sample is ~50μm thick100μm

Compensated coils for magnetization measurements

Sample outSample in

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USb2 extraction coil magnetometry clearly shows AFM transition

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USb2 phase diagram matches well between magnetostriction and magnetization

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Established first H-T phase diagram of USb2.

Magnetostriction and magnetization phase boundaries agree.

High-field, low-temperature magnetic state still unclear (ie. PM or canted-AFM) due to field limitation.

Quantum oscillations to see Fermi surface above Hc?

Experiment on UBi2 to see possible Fermi surface effects.

Conclusions and Future Work

Thank You!

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Quantitative analysis via corrected background gives magnetic moment smaller by ~0.8μB

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USb2 AFM transition in magnetostriction along the c axis downsweep

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High field magnetostriction along c-axis

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Structures of all UX2 compounds

D. Aoki et al., Phil. Mag. B, 80, 1517 (2000)